1. Field of the Invention
The present invention relates to a drawing apparatus, a data processing method, and a method of manufacturing an article.
2. Description of the Related Art
A drawing apparatus which performs drawing on a substrate while scanning a beam such as a charged particle beam (for example, an electron beam or an ion beam) or a light beam is available. It is a common practice in the drawing apparatus to divide a region to be drawn into a plurality of partial regions to have overlap regions in which the partial regions overlap each other, and patterns are drawn in the plurality of partial regions with the beam. Such a scheme is called the stitching scheme. Drawing in an overlap region is done with two or more partial regions sharing the overlap region. Hence, when two partial regions share an overlap region, a pattern is drawn in the overlap region at a dose half that in the remaining region in drawing within each partial region.
As methods of controlling the dose, the time modulation and spatial modulation types are available. The time modulation method is used to control the time to irradiate a substrate with a beam, and is also called PWM (Pulse Width Modulation). The spatial modulation method is used to form a pattern using a plurality of pixels, and control the area density of pixels to be irradiated with a beam while keeping constant the time to irradiate each pixel with the beam. The spatial modulation method is described in “Proc. of SPIE Vol. 7970 79701AProc. (2011)”.
An example in which binary pattern data to control drawing is generated by the spatial modulation method will be described with reference to FIGS. 8 to 12. Reference numeral 801 denotes the schematic structure of design pattern data obtained by arranging a design pattern on a pixel coordinate system defined in a drawing apparatus. In this example, the design pattern represented by the design pattern data 801 is a 20 nm×20 nm square pattern designed using a 0.25-nm grid, and pixel coordinates are given at a pixel pitch of 2.5 nm. Since the design grid is narrower than the pixel pitch, the design pattern cannot be faithfully displayed on a pixel coordinate system.
For this reason, the area density of a design pattern in each pixel is calculated, and the dose in each pixel is determined based on the obtained area density to generate multilevel pattern data. Reference numeral 802 denotes the schematic structure of the thus generated multilevel pattern data. Note that the dose (fixed value) of a beam per pixel in the drawing apparatus is assumed to be “10”, while the dose (fixed value) per pixel in design pattern data 810 is assumed to be “8”. Since the dose (fixed value) per pixel in the drawing apparatus is “10”, multilevel pattern data is transformed into binary pattern data using an error diffusion method to control the dose of a design pattern at the density of pixels in which the beam is ON. As the error diffusion method, the Floyd & Steinberg error diffusion method, for example, can be adopted.
More specifically, binarization errors are distributed to peripheral pixels to be processed, in accordance with an error diffusion matrix (error diffusion kernel) shown in FIG. 12, while binarizing the value of a pixel of interest upon sequentially focusing attention on a plurality of pixels of the multilevel pattern data 802. The selection order of pixels of interest (the direction to progress transformation) can be determined by, for example, selecting the upper left pixel first, and performing raster scanning of subsequent pixels. If the value of a pixel of interest is smaller than 5, the binarization result of this pixel is set to “0”; otherwise, the binarization result of this pixel is set to “10”. With such processing, binary pattern data is generated. Reference numeral 803 denotes the schematic structure of the thus generated binary pattern data.
Reference numeral 804 denotes the schematic structure of a drawing image (a latent image formed on a resist) drawn while controlling a beam in accordance with the binary pattern data 803. Note that the beam size is set sufficiently larger than a pixel with a size of 2.5 nm×2.5 nm to smooth a pattern formed in accordance with the density of pixels.
For an overlap region as mentioned above (doubly drawn region), multilevel pattern data 805 for double drawing is generated. A pixel in the multilevel pattern data 805 for double drawing has a value half that of a pixel in the multilevel pattern data 802 for one-time drawing. The multilevel pattern data 805 for double drawing is binarized in accordance with the above-mentioned method to generate binary pattern data 806 for double drawing. The density of pixels (ON pixels) having a value of “10” in the binary pattern data 806 for double drawing is lower than that in the binary pattern data 803 for one-time drawing. A pattern is drawn in an overlap region twice in accordance with the binary pattern data 806 for double drawing. Reference numeral 807 denotes the schematic structure of a drawing image drawn while controlling a beam in accordance with the binary pattern data 806.
The drawing image 807 formed by double drawing has a fidelity to the design pattern data 801, which is lower than that of the drawing image 804 formed by one-time drawing. With this arrangement, in the spatial modulation method, when an overlap region is provided to perform double drawing, the reproducibility of an actual drawing image to a design pattern degrades.